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<title>Problem 1914. -- [Usaco2010 OPen]Triangle Counting 数三角形
</title><center><h2>1914: [Usaco2010 OPen]Triangle Counting 数三角形
</h2><span class=green>Time Limit: </span>10 Sec&nbsp;&nbsp;<span class=green>Memory Limit: </span>64 MB<br><span class=green>Submit: </span>146&nbsp;&nbsp;<span class=green>Solved: </span>79<br>[<a href='submitpage.php?id=1914'>Submit</a>][<a href='problemstatus.php?id=1914'>Status</a>][<a href='bbs.php?id=1914'>Discuss</a>]</center><h2>Description</h2><div class=content>在一只大灰狼偷偷潜入Farmer Don的牛群被群牛发现后，贝西现在不得不履行着她站岗的职责。从她的守卫塔向下瞭望简直就是一件烦透了的事情。她决定做一些开发智力的小练习，防止她睡着了。想象牧场是一个X，Y平面的网格。她将N只奶牛标记为1…N (1 <= N <= 100,000)，每只奶牛的坐标为X_i,Y_i (-100,000 <= X_i <= 100,000;-100,000 <= Y_i <= 100,000; 1 <= i <=N)。然后她脑海里想象着所有可能由奶牛构成的三角形。如果一个三角形完全包含了原点(0,0)，那么她称这个三角形为“黄金三角形”。原点不会落在任何一对奶牛的连线上。另外，不会有奶牛在原点。给出奶牛的坐标，计算出有多少个“黄金三角形”。顺便解释一下样例，考虑五只牛，坐标分别为(-5,0), (0,2), (11,2), (-11,-6), (11,-5)。下图是由贝西视角所绘出的图示。
<img border="0" src="images/1914_1.jpg"> 
</div><h2>Input</h2><div class=content>第一行:一个整数: N
第2到第N+1行: 每行两个整数X_i，Y_i，表示每只牛的坐标

</div><h2>Output</h2><div class=content>* 第一行: 一行包括一个整数，表示“黄金三角形的数量”
</div><h2>Sample Input</h2>
			<div class=content><span class=sampledata>5<br />
-5 0<br />
0 2<br />
11 2<br />
-11 -6<br />
11 -5<br />
<br />
<br />
<br />
</span></div><h2>Sample Output</h2>
			<div class=content><span class=sampledata>5</span></div><h2>HINT</h2>
			<div class=content><p></p></div><h2>Source</h2>
			<div class=content><p><a href='problemset.html?search=Gold'>Gold</a></p></div><center>[<a href='submitpage.php?id=1914'>Submit</a>][<a href='problemstatus.php?id=1914'>Status</a>][<a href='bbs.php?id=1914'>Discuss</a>]</center>﻿<br>

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